Question: At what opera did librettist Philip Glass play in?
Paraphrase: Librettist Philip Glass was in what opera?
SPARQL (Wikidata):  select distinct ?sbj where { ?sbj wdt:P87 wd:Q189729 . ?sbj wdt:P31 wd:Q1344 } 
Answer: Akhnaten, Einstein on the Beach, Satyagraha, La Belle et la Bête, The Perfect American